import random
alaph="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
temp=[]
str=""
for i in range(0,4):
    temp.append(1)
    temp[i]=alaph[random.randint(0,len(alaph)-1)]
    str=str+temp[i]
print(str)